Make a supersaturated solution by stirring the Epsom salt (solute) into warm tap water (solvent) inside the beaker. If the salt doesn't dissolve completely, have an adult help you microwave it for about 30 seconds. Carefully remove it, and stir it again.
Add the dishwashing soap and stir again.
Use the lens cloth to "wash" the solution onto a glass window or mirror. Dab away the excess to avoid drips.